Chickens have 2 feet. Rabbits have 4 feet.
So kids can either draw or play around to match up heads and feet. Initially, we have at least 17x2=34 feet, becasue each has at least 2 feet, and so 48-34=14 feet remain. These remaining feet must belong to the rabbits. Once they are added, 10 heads have two feet and are chickens, and the remaining 7 heads with four feet are rabbits.
Additional Methods (if equations of lines have already been covered)
Let x = the number of rabbits and y = the number of chickens. Then we have x + y =17 heads and 4x + 2y = 48 feet. Students can solve this problem a number of ways, such as